Fabricating self-lubricating articles



April 13, 1965 J. A. REYNOLDS ETAL 3,177,564

FABRICATING SELF-LUBRICA'IING ARTICLES Filed March 25, 1963 InventorAttorneys United States Patent Ofilice 3,177,564 Patented Apr. 13, 19653 177 564 FAaarcArrNe sarr rohmoArrNe ARTICLES Jefiirey Alan Reynoldsand David Hall, Lcarnington Spa, England, assignors, by mesneassignments, to Gert Deventer, Munich, Germany Filed Mar. 25, 1963, Ser.No. 267,500 Claims priority, application Great Britain, Mar. 28, 1962,11,86W62 9 Claims. (Cl. 29-1825) The present invention relates toamethod of and apparatus for fabricating self-lubricating articles orcomponents which comprise a layer-lattice solid lubricant incorporatedin a powder metal matrix, and to articles or components made by themethod.

Such articles are at present fabricated as a graphitecontaining metalpowder moulding comprising a consolidated mass of a metal powder orpowders comprising mixed grain sizes up to about 60 microns andcolloidal graphite, the mixture having been sintered and compressedwhereby the metal structure is stabilised with the colloidal graphitetrapped under pressure in the interstices of the metal matrix, themoulding being machined to the shape and dimensions of the requiredarticle or component. The production of such mouldings is described inUnited States specification No. 2,974,039 and British specification Nos.892,846 and 892,847. The principal metal powder comprises iron, copper,aluminum and/ or nickel, separately or in combination, to which may beadded secondary metal powders such as zinc, tin, lead and cadmium, aloneor in combination.

The present invention has for an object to reduce the cost of sucharticles and components by using the special self-lubricating materialto provide only the hearing or wearing surface of the article orcomponent, the self-lubricating material being bonded as a layer on asupport comprising a metal backing sheet or strip which provides therequired mechanical support for the self-lubricating layer.

From one aspect, the invention consists in a method for the manufactureof self-lubricating articles or components comprising intimately mixingone or more metal powders, comprising mixed grain sizes of up to about60 microns, with a powdered solid lubricant comprising colloidalgraphite and/ or molybdenum disulphide and/ or boron nitride (thelubricant occupying 3% to 50% of the total volume), loosely spreadingthe powder mixture in a layer on the surface of a metal backing strip,heating the backing strip, with the powder layer thereon, in anatmosphere which avoids undesirable oxidation or r action with thepowder, to a sintering temperature below the melting point of theprincipal metal powder constiutent, rolling the strip with the powderlayer thereon between rolls to compact the layer, and further heatingthe rolled composite strip, whereby to produce an annealed dense andcoherent layer, comprising the metal powder matrix with the solidlubricant incorporated in the interstices of the matrix, which is bondedto the surface of the metal backing strip. The composite strip can besubmitted to fabricating operations, such as blanking, forming andmachining, to produce bearing shells, thrust washers, or othercomponents.

In one embodiment of the method according to the invention, a strongmetal backing strip, for example, of mild steel, is cleaned and, ifnecessary, copper plated prior to loosely spreading the powder mixtureon the surface of the metal backing strip to the desired thickness. Thepowder mixture may comprise 79 /2 copper,

19 /2% tin and 8% graphite, the percentages being given by Weight. Thebacking strip, with the powder thereon, is heated in an atmosphere whichavoids undesirable oxidation or reaction with the powder, to a sinteringtemperature below the equilibrium solidus of the alloy formed from themetal powder mixture concerned, for example between 600 and 750 C., and,after withdrawal from the furnace and being cooled, is then rolled tocompact the powder layer. The composite strip is'then submitted to afurther heat treatment to develop the bond between the metal powdergrains, and between the metal powder grains and the backing strip, andto relieve the stresses in the metal powder matrix. The composite stripcan then be submitted to conventional fabricating operations, such asblanking, forming and machining, in order to produce bearing shells,thrust washers or other components.

From another aspect the invention consists in an article or componenthaving a self-lubricating surface and comprising a sheet metal backingon to at least one surface of which is roll-bonded a substantially denseand coherent layer, comprising a sintered metal matrix in theinterstices of which is incorporated a layer-lattice solid lubricant,the lubricant occupying 3% to of the total volume of the layer.

The invention further consists in an apparatus for carrying out theprocess.

In order that the invention may be more clearly understood, referencewill now be made to the accompanying drawing, in which:

FIGURE 1 is a diagrammatic side view of an apparatus for carrying outthe process of this invention.

FIGURE 2 is a section along the line AA in FIG- URE 1.

FIGURE 3 is a plan view of the spreading arrangement, with the hopperremoved.

FIGURE 4 is a perspective view of a shell bearing according to thisinvention.

Referring to the drawing, a mild steel backing strip 1 is fed from thecoil 1a by driven straightening rollers 2, and, after being fed past thespreading device generally indicated by 3 where the powder mixture 7 isloosely spread on the surface of the strip, passes through a sinteringfurnace 4. After leaving the sintering furnace, the strip with thepowder layer 7 thereon is rolled between rollers 5 to consolidate thepowder into a compact layer on the surface of the metal backing strip.After leaving the rollers 5 the composite strip passes through anannealing furnace 6. The composite strip is drawn from the annealingfurnace by pull-out rollers 8 and may then be cut into desired lengths,wound on to a roll or directly fed to machines for fabricating thecomponents to be made.

In the spreading device 3 the powder mixture 7 is fed to the uppersurface of the strip 1 from a hopper 9. The strip 1 moves in thespreading device on an endless belt 10 which is wider than the srip 1and is supported by the rigid table 11. The strip is located laterallywith respect to the hopper by means of inverted L-shaped guides 12supported above the belt 10. The hopper 9 which is carried by the guides12, has an outlet 9a which is of a depth to provide a layer of powder 7on the strip exceeding the thickness of the required loosely spreadlayer. The side walls of the guides 12 keep the power 7 on the strip,leaving side zones thereof uncovered by the powder. The powder layer isspread to cover these sides zones and to produce the powder layer of therequired thickness by a generally V-shaped spreading blade or plough 313, excess powder being deflected over the sides of the metal backingstrip 1 and on to the surface of the belt 10. The powder which falls onto the belt is discharged into a collecting device 14 for feeding backto the is weak, and the compacted layer can be easily scratched andscraped oif the backing strip.

The rolled strip is then passed through an annealing furnace 6 which maybe similar to the sintering furnace 4, in which the powder is againheated to about hopper 9.

The furnace 4-, having refractory walls 15, may be the same temperatureas in the sintering furnace 4. heated in any suitable manner by heatingmeans generally This annealing treatment develops the bond between theindicated at 16. The metal strip with the powder metal power grains, andbetween the grains and the thereon pa ses through a muffle 17 in thefurnace havbacking strip, and relieves the stresses within the comingwalls of a heat-resisting alloy, such as Inconcl, 1Q pacted layer. Uponleaving the annealing furnace the the nuflie containing an atmospherewhich avoids unmetal grains have been firmly welded to each other anddesirable oxidation or reaction with the powder, for ex- [0 th backingstrip, producing a substantially dense ample an atmosphere of r ked o iwhi h may and coherent layer, comprising the metal powder matrix be fedinto th fii i th inlet 18, Excess gas with the solid lubricantincorporated in the interstices is burnt at the ends of the muffie. Theoutlet end of the of the matrix, Which is bonded to the Surface f hmufiie is provided with a water-cooled chill plate 19 maifli backing P-The layer is resistant to Scratch beyond th nd f the furnace h b Th i lt nd ing and the composite strip will withstand fabricating opof themuffle may also have a water-cooling passage 21) Bunions, to Produce,for p Shell hearings Such as therearound. shown in FIGURE 4.

The furnace should be arranged so that the tempera- If the si teredpowder layer on the backing strip is ture of the powder will not beraised too quickly to the foiled instead of Cold, the Separate annealingsintering temperature. The time required to reach the nace may bedispensed with provided the rolling is sintering temperature should beat least 1 minute, prefereiiected ill a reducing P The T0115 y ably notless than 1 /2 minutes, in order to avoid crackp he located in theSihtfifihg iumflce- It is ing of the powder layer. To achieve thi h fu25 portant however, that the stresses in the compacted layer chamber canconveniently be about 9 feet long when Should be relievedthe metal stripis fed at a speed of 3 feet per minute. In 0116 Particllhir example, thePowder mixture The heating means 16 may be divided into sections prises791/2% PP 121/270 tin and 8% coiioidai p which may be separatelycontrolled to regulate the rate he, the Percentages hfiihg given yWeight The metal of rise of temperature. Any powder which may f llpowders have mixed grain sizes of from 5 to 60 microns off the strip inthe muffle is collected in a box 21 in the and are Preferably ofirregular P The metal P floor of the muffle, the bottom of which can beopened and graphite are intimately mixed before being fed toperiodically to empty the collected powder. The box the pp The mildSteel Strip 1 y be about 21 should be located at a position where thetemperathick and has its Surface, 011 Which the Powder ture is notsufficiently high to melt the powder. The is to Spread, PP P The 10056P0Wder layer strip after being maintained at the sintering temperay haveathickness of ",w h aft r si t rt fo a short i h passes i the coolingZone ing and rolling is reduced to a thickness of about 0.040.". andover the n plate 19 and is cooled Substantially The strip and powder areheated in the sintering furnace before leaving the mufih to about 725 C.in about 2 /2 minutes, and are held The Strip 1 with the Sintered powder7 thereon is 40 at th1s temperature for about /2 minute before beingthen rolled cold by the rollers 5 so as to reduce the quickly cooled byPassmg over the.chln plate. The thickness of the powder layer and toimprove the metal temlgeramre to Winch the pfwder 1s heated m theto-metal contact between the metal powder grains and funiace 13 also 725Similar Slillfifill" and annealin tem eratures are suitbetween the metalpowder grains and the backing strip, r g P b f f Th rd 1 b t m th bt t.)able for a powder mixture of 77 /2% copper, 12 /2% Y 19mlJ 0 6 so 1 Inere e Ween tin and 10% graphite, percentages being given by weight.whereby P siibstantlaliy fully compacted layer- Other compositions ofpowder mixtures are possible. The reductlon the thlckmss of the Powderlayer may Various compositions which may be used are shown in be about80%. the following table. The figures in brackets refer to At this Stagethe bond hfitweel'l the metal Powder weight percentages, except whereotherwise stated, and are grains, and between the grains and the backingstrip, maxi a,

Group Principal Metal Powder Secondary Additions Lubricants binationwith- Cu, Fe, Al, separately or combined, or further combined with Cu,in combination with Fe, in combination with Al, in combination with- Ni,separately or in com- Graphite, BN, M08: or any combination of these provided the total lies between 350% by volume of the finished compact.

Zn, Sn, Pb, Cd, Sb, Be, Mn,

separately or in any combination provided that the total does not exceed15% with 0ptionally up to 5% Indium in Fe(2). Pb and/or In(15)separately or in any combination but not in total exceeding of themetallic content.

The backing strip should be made or plated with a metal which bonds withthe metal grains of the powder mixture. For a mixture of which aluminiumis the principal metal powder, the backing strip is preferably ofaluminium.

If high percentages of lubricants (for example 12% or more) are to beincorporated, the colloidal lubricant grains (of about 1 micron) arefirst agglomerated by cold pressing, the agglomerate being comminuted toproduce granules of about 200 to 500 microns which are then mixed withthe metal powder or powders.

The backing strip can be provided with a compacted layer on bothsurfaces by submitting a composite strip having a compacted layer on onesurface to a second treatment to provide a compacted layer on the othersurface of the backing strip.

We claim:

1. The method for the manufacture of self-lubricating articles,comprising intimately mixing at least one metal powder, comprising mixedgrain sizes of up to about 60 microns, with a powdered solid lubricantselected from the group consisting of colloidal graphite colloidal,molybdenum disulphide and colloidal boron nitride, the lubricantoccuping 3% to 50% of the total volume of the mixture, loosely spreadingthe powder mixture in a layer on the surface of a metal backing strip,heating the backing strip, with the powder layer thereon, in anatmosphere which avoids undesirable oxidation and reaction with thepowder, to a sintering temperature below the melting point of theprincipal metal powder constituent, rolling and further heating thestrip with the powder layer thereon until an annealed dense and coherentlayer is produced, comprising a metal powder matrix with discreteparticles of the solid lubricant incorporated in the interstices of thematrix, which is bonded to the surface of the metal backing strip.

2. The method as claim in claim 1, wherein after heating to thesintering temperature, the strip and powder layer are cooled beforerolling, and the rolled composite strip is submitted to a further heattreatment to develop the bond between the metal powder grains, andbetween the metal powder grains and the backing strip, and to relievethe stresses in the metal powder matrix.

3. The method as claimed in claim 1, which consists in heating thepowder layer at a rate such that the time required to reach thesintering temperature in at least 1 minute.

4. The method as claimed in claim 1, wherein the rolling produces areduction in the thickness of the loose powder layer of about 80%.

5. Method for the manufacture of self-lubricating articles whichconsists in intimately mixing at least one metal powder comprising mixedgrain sizes of up to about 60 microns, with a powdered solid lubricantselected from the group consisting of colloidal graphite, colloidalmolybdenum disulphide and colloidal boron nitride, the lubricantoccupying 3% to 50% of the total volume of the mixture, looselyspreading the powder mixture in a layer on the surface of a metalbacking strip, heating said backing strip with the powder layer thereonin a reducing atmosphere to a sintering temperature below the meltingpoint of the principal metal powder constituent and at a rate such thatthe time required to reach the sintering temperature is at least oneminute, cooling the strip with the sintered powder layer thereon,rolling the strip with the sintered powder layer thereon, to compact thelayer and eliminate substantially all voids, submitting the rolledcomposite strip to further heat treatment to develop the bond betweenthe metal powder grains and between the metal powder grains and thebacking strip, and to relieve the stresses in the metal powder matrix,whereby to produce an annealed dense and coherent layer, comprising themetal powder matrix with discrete particles of the 6 solid lubricantincorporated in the interstices of the matrix, which is bonded to thesurface of the metal backing strip.

6. An article having a self-lubricating surface and consisting of asheet metal backing on to at least one sur face of which is bonded asubstantially dense and coherent layer consisting of a sintered powdermetal matrix of non-interconimunicating cells containing discreteparticles of a layer-lattice solid lubricant, the lubricant occupying 3%to 50% of the total volume of the layer.

7. Apparatus for the manufacture of self-lubricating articles accordingto claim 6, comprising a powder spreading device including an endlessconveyor belt, of which the upper run is adapted to support the metalbacking strip, two L-shaped guides extending above and longitudinally ofthe conveyor belt to define a guideway for the metal backing strip, apowder hopper above said guides and arranged to feed powder between saidguides to a predetermined thickness, and a plough arranged downstream ofsaid hopper and adapted to spread the powder on the metal strip to athickness less than said predetermined thickness and to deflect theexcess powder on to said conveyor belt; a sintering furnace including atubular mutfie, heating means comprising separate sections forregulating the heat along said mufile, a chill plate at the end of saidmufile for chilling the metal strip and the powder layer thereon;compacting rolls for compacting the powder layer on said strip; anannealing furnace including a tubular muffle; and mean for feeding themetal backing strip successively through said spreading device, saidsintering furnace, said compacting rolls, and said annealing furnace.

8. In apparatus for making articles according to claim 6, a powderspreading device comprising an endless conveyor belt, of which the upperrun supports the metal backing strip, two L-shaped guides extendingabove and longitudinally of the conveyor belt to define a guideway forthe metal backing strip, a powder hopper above said guides and arrangedto feed powder between said guides to a predetermined thickness, and agenerally V-shaped plough arranged downstream of said hopper and adaptedto spread the powder on the metal strip to a thickness less than saidpredetermined thickness and to deflect the excess powder on to saidconveyor belt.

9. Method for the manufacture of self-lubricating articles whichconsists in intimately mixing about to by weight of powdered copper andabout 10% to 15% by weight of powdered tin, said metal powderscomprising mixed grain sizes of up to about 60 microns, with about 8% to12% by weight of colloidal graphite, loosely spreading the powdermixture in a layer on the copperplated surface of a mild steel backingstrip, heating said backing strip with the powder layer thereon in areducing atmosphere to a temperature of about 725 C. in a time of from 1to 3 minutes cooling the strip with the powder layer thereon, rollingthe strip with the powder layer thereon between rollers to reduce thethickness of the layer to about 20% of its original thickness, heatingthe rolled composite strip to about 725 C. to develop the bond betweenthe metal powder grains and between the metal powder grains and thebacking strip, and to relieve the stresses in the metal powder matrix,whereby to produce an annealed dense and coherent layer, comprising thecopper-tin metal powder matrix with the colloidal graphite incorporatedin the interstices of the matrix, which is bonded to the copper-platedsurface of the backing strip.

References Cited in the file of this patent UNITED STATES PATENTS2,198,253 Koehring Apr. 23, 1940 2,198,254 Koehring Apr. 23, 19402,299,877 Calkins Oct. 27, 1942 2,815,567 Gould et al Dec. 10, 19572,086,464 Lewis et al. May 30, 1961

1. THE METHOD FOR THE MANUFACTURE OF SELF-LUBRICATING ATRICLES,COMPRISING INTIMATELY MIXING AT LEAST ONE METAL POWDER, COMPRISING MIXEDGRAIN SIZES OF UP TO ABOUT 60 MICRONS, WITH A POEDERED SOLID LUBRICANTSELECTED FROM THE GROUP CONSISTING OF COLLODIAL GRAPHITE COLLOIDAL,MOLYBDENUM DISULPHIDE AND COLLOIDAL BORON NITRIDE, THE LUBRICANTOCCUPING 3% TO 50% OF THE TOLAT VOLUME OF THE MIXTURE, LOOSELY SPREADINGTHE POWDER MIXTURE IN A LAYER ON THE SURFACE OF A METAL BACKING STRIP,HEATING THE BACKING STRIP, WITH THE POWDER LAYER THEREON, IN ANATMOSPHERE WHICH AVOIDS UNDERSIRABLE OXIDATION AND REACTION WITH THEPOWDER, TO A SINTERING TEMPERATURE BELOW THE MELTING POINT OF THEPRINCIPAL METAL POWDER CONSTITUENT, ROLLING AND FURTHER HEATING THESTRIP WITH THE